1. Field of the Invention
The invention relates to an improved process for manufacturing an olefin polymer composition, in particular polyethylene, that incorporates two or more reaction zones in an optimized configuration that improves product transitions and provides improved reactor quality control.
2. Description of the Prior Art
The general use of two reactors in series to manufacture an olefin polymer composition is described in the prior art and further advanced by U.S. Pat. No. 6,586,537, the disclosure of which is incorporated herein by reference in its entirety. In the '537 patent, a process is described that is suitable for production of olefinic polymer grades including ethylene polymer compositions comprising a polymer (A) and a polymer (B) having differing comonomer content and differing molecular mass. Such polymer grades are referred to in the industry as “bimodal” or “multimodal” grades. The use of two reactors in series to produce bimodal PE grades and their specific advantages are disclosed in U.S. Pat. No. 6,225,421 (Solvay Polyolefins), the disclosure of which is incorporated herein by reference in its entirety. The use of an intermediate-pressure light-gas removal system between two reaction zones that makes use of a fractionator is disclosed in WO 2006/015807, the disclosure of which is incorporated herein by reference.
General polymer sampling systems are well known and applied in the art, for example, U.S. Pat. Nos. 3,556,730, 4,469,853, 6,037,184, and 6,042,790, as well as WO/05080441.
In the multi-reactor systems disclosed in the prior art, the optimization of transitions between bimodal and monomodal products and methods by which the first reactor might be sampled and analyzed for quality control are neither taught nor suggested.
The present invention provides an optimized process which can be used for the manufacture of bimodal or monomodal grades using a wide range of catalysts, including Ziegler or chromium catalysts that overcomes the deficiencies of the prior art systems.